This invention relates to the processing of bilirubin-containing substances such as plasma and serum. In particular, it is concerned with reclaiming plasma or serum which has become green in color due to bilirubin oxidation as well as maintaining the proper color after reclamation and during storage or processing. The term "reclamation" means elimination of the biliverdin pigment in the fluid, ordinarily by converting biliverdin to a substance having an adsorption spectrum similar or identical to that of bilirubin. The primary focus of the invention is upon the manufacture and stabilization of serum intended for use as controls, calibrators or standards in analytical methods.
Bilirubin is a bile pigment structurally related to hematoporphyrin and hematin. It forms complexes with proteins such as albumin found in serum and contributes to the characteristic straw yellow color or normal plasma or serum. Exposure of plasma or serum to oxygen under certain conditions can result in the oxidation of bilirubin to biliverdin, along with a concomitant color change from yellow to green. This problem is particularly acute with out dated plasma and serum derived therefrom by defibrination. This serum is unmarketable for use in clinical laboratories because of its objectional color.
U.S. Pat. No. 4,201,694 discloses increasing the shelf-life of a serum bilirubin reference composition by adjusting the serum pH to between about 8.3 and 9.5 and providing a sulfhydryl compound to further enhance the bilirubin stability.